The statements in this section merely provide background information related to the present disclosure and may not constitute prior art
The present disclosure is related in general to wellsite surface equipment such as wireline surface equipment and the like. When using downhole cables, such as wireline cables, in high-pressure wellbores, measures must be taken to prevent release of that pressure when running cable in and out of the wellbore.
Wellhead pressure is typically controlled by passing the cable 12 run from a wireline truck 13 or the like through a combination of pulleys, masts, and/or risers, (not shown), one or more elongated grease tubes or flow tubes 14, and a packoff assembly or “stuffing box” (not shown). As the well pressure from the wellbore 10 enters the flow tubes 14, grease is injected at a location 16 near the bottom of the tube 14 at a pressure greater than a measured well pressure. The grease then exits a top portion of the tube 14 and is discarded. In the packoff assembly is tightened down by hydraulic means or the like onto a rubber gasket, which causes the gasket to squeeze onto and seal against the wireline cable. The packoff assembly provides a static seal against a conventional wireline cable. When raising or lowering the cable, contact between the cable 12 and the sealing surface may cause the cable's outer armor wires to saw against the seal's rubber surface.
The drawbacks of the flow tubes 14 are related primarily to the tight tolerances (about 0.003 to about 0.005 inches) required between the interior of the tubes 14 and the exterior of the wireline cables 12. At these tight tolerances, armor wires raised up above the cable 12 profile can lead to armor crossover, armor wire milking (wherein a raised armor is pushed down the cable 12), and bird caging (wherein several raised armor wires become tangled above the cable profile). Sand and rocks from the wellbore may also become embedded between the armor wires and further exacerbate these problems. In addition, because these grease tubes or flow tubes 14 are disadvantageously placed above the lubricators and other pressure control equipment at a relatively inaccessible location high above the well floor that may only be reached by the use of personnel baskets or the like. Furthermore, traditional wireline cables 12 may have uneven profiles and slight inconsistencies in outside diameter, which require higher flow tube 14 tolerances, which causes inefficient sealing and great use of grease. Flow tubes 14 used in sealing the cable 12 at the wellhead must be chosen based on the largest outside diameter, creating a weaker seal when the diameter is at its smallest dimension.
In another pressure-sealing strategy, smooth-profile cables 20 (see FIGS. 3 and 4) are used in conjunction with rubberized cylindrical packers or wipers 22, which are sized to fit tightly over the cable 20 rather than the long lengths of grease tubes or flow tubes 14. The packers 22, however, may become damaged with prolonged use, especially on the tapered ends thereof (see FIG. 4).
It remains desirable to provide improvements in wellsite surface equipment in efficiency, flexibility, reliability, and maintainability.